I have an '01 S10 4.3 2wd with 180k+ miles. I think the transmission is slipping from 3 to 4 and also during downshifting for passing gear. There is also a very brief hesitation at highway speed every 10-20 miles which I've never noticed in a vehicle before. It may be unrelated, but my oil pressure also moves around. It's worse at idle and it goes up to normal when moving. It's not leaking any oil. I'd love to send you video of the dash display.
starting up cold
https://www.youtube.com/watch?v=fQSojY-1PG4
on the way home after the cold start and about 5 minute dwell time
https://www.youtube.com/watch?v=9guRPMQXx9k
classic signs of a failing transmission. It won't be long now. The slipping is going to eat the rest of the clutch until it breaks free and you will have no more gears and glittery sludge for fluid.
Sounds like the engine is not too far behind either.
